POR C of Arabidopsis thaliana: a third light- and NADPH-dependent protochlorophyllide oxidoreductase that is differentially regulated by light

During the sequencing of the genome of Arabidopsis thaliana a gene has been identified that encodes a novel NADPH-protochlorophyllide oxidoreductase (POR)-like protein (accession number AC 002560). This protein has been named POR C. We have expressed the POR C protein in Escherichia coli and have determined its in vitro activity. POR C shows the characteristics of a light-dependent and NADPH-requiring POR similar to POR A and POR B. The expression of the POR C gene differs markedly from that of the POR A and POR B genes. In contrast to the POR A and POR B mRNAs, the POR C mRNA has been shown previously to accumulate only after the beginning of illumination. In light-adapted mature plants only POR B and POR C mRNAs were detectable. The amounts of both mRNAs show pronounced diurnal rhythmic fluctuations. While the oscillations of POR B mRNA are under the control of the circadian clock, those of POR C mRNA are not. Another difference between POR B and POR C was found in seedlings that were grown under continuous white light. The concentration of POR C mRNA rapidly declined and soon dropped beyond the limit of detection, after these seedlings were transferred to the dark. On the other hand, POR B mRNA was unaffected by this light/dark shift. When seedlings were exposed to different light intensities, the amounts of POR B mRNA remained the same, while POR A and POR C mRNAs were modulated in an inverse way by these light intensity changes. POR A mRNA was still detectable in seedlings grown under low light intensities but disappeared at higher light intensities, while the mRNA concentration of POR C rose with increasing light intensities. These different responses to light suggest that the functions of the three PORs of Arabidopsis are not completely redundant, but may allow the plant to adapt its needs for chlorophyll biosynthesis more selectively by using preferentially one of the three enzymes under a given light regime.     

Bone morphogenetic protein receptor signaling is necessary for normal murine postnatal bone formation

Functions of bone morphogenetic proteins (BMPs) are initiated by signaling through specific type I and type II serine/threonine kinase receptors. In previous studies, we have demonstrated that the type IB BMP receptor (BMPR-IB) plays an essential and specific role in osteoblast commitment and differentiation. To determine the role of BMP receptor signaling in bone formation in vivo, we generated transgenic mice, which express a truncated dominant-negative BMPR-IB targeted to osteoblasts using the type I collagen promoter. The mice are viable and fertile. Tissue-specific expression of the truncated BMPR-IB was demonstrated. Characterization of the phenotype of these transgenic mice showed impairment of postnatal bone formation in 1-mo-old homozygous transgenic mice. Bone mineral density, bone volume, and bone formation rates were severely reduced, but osteoblast and osteoclast numbers were not significantly changed in the transgenic mice. To determine whether osteoblast differentiation is impaired, we used primary osteoblasts isolated from the transgenic mice and showed that BMP signaling is blocked and BMP2-induced mineralized bone matrix formation was inhibited. These studies show the effects of alterations in BMP receptor function targeted to the osteoblast lineage and demonstrate a necessary role of BMP receptor signaling in postnatal bone growth and bone formation in vivo.     

rmlB基因在单核细胞增生李斯特菌耐药性、生物被膜形成和毒力方面的作用

【目的】探究单核细胞增生李斯特菌(Listeria monocytogenes,Lm)rmlB基因在细菌耐药、生物被膜形成和毒力方面的作用。【方法】通过同源重组的方法敲除Lm染色体上的rmlB基因,比较野生株与rmlB缺失株在耐药性方面的差异;利用微孔板法观测rmlB缺失菌株生物被膜形成能力的变化;利用RT-PCR检测缺失菌株中主要毒力基因转录表达,并观察rmlB缺失对细菌溶血活性的影响。【结果】同野生菌株相比,rmlB缺失菌株对头孢菌素和杆菌肽等作用位点在细菌细胞壁和细胞膜的敏感性显著增加(P≤0.01),生物被膜形成能力显著降低(P≤0.01),细菌主要毒力基因hly的转录表达及溶血活性也发生显著降低(P≤0.01)。【结论】rmlB基因在Lm生物被膜形成和耐受作用位点位于细胞壁和细胞膜的抗生素及细菌毒力方面具有重要作用。     

New bioengineering insights into human neural precursor cell expansion in culture

Understanding initial cell growth, interactions associated with the process of expansion of human neural precursor cells (hNPCs), and cellular events pre- and postdifferentiation are important for developing bioprocessing protocols to reproducibly generate multipotent cells that can be used in basic research or the treatment of neurodegenerative disorders. Herein, we report the in vitro responses of telencephalon hNPCs grown in a serum-free growth medium using time-lapse live imaging as well as cell-surface marker, aggregate size, and immunocytochemical analyses. Time-lapse analysis of hNPC initial expansion indicated that cell-surface attachment in stationary culture and the frequency of cell-cell interaction in suspension conditions are important for subsequent aggregate formation and hNPC growth. In the absence of cell-surface attachment in low-attachment stationary culture, large aggregates of cells were formed and expansion was adversely affected. The majority of the telencephalon hNPCs expressed CD29, CD90, and CD44 (cell surface markers involved in cell-ECM and cell-cell interactions to regulate biological functions such as proliferation), suggesting that cell-surface attachment and cell-cell interactions play a significant role in the subsequent formation of cell aggregates and the expansion of hNPCs. Before differentiation, about 90% of the cells stained positive for nestin and expressed two neural precursor cells surface markers (CD133 and CD24). Upon withdrawal of growth cytokines, hNPCs first underwent cell division and then differentiated preferentially towards a neuronal rather than a glial phenotype. This study provides key information regarding human NPC behavior under different culture conditions and favorable culture conditions that are important in establishing reproducible hNPC expansion protocols.     

Advances in soil microbial ecology and the biodiversity

Recent studies on the colony formation of soil bacteria opened the way to categorize soil bacteria into colony forming curve (CFC) groups of different growth rates. A bacterial culture collection comprising organisms from every CFC group is called an ecocollection. Outlines of ECs of paddy soil 1992 and grassland soil 1987 and 1992 were described. Phylogenetic studies by 16S rDNA sequencing showed a great diversity of culture strains of the ecocollections (EC). A set of alternative concepts was proposed; the active and the quiescent forms of bacterial cells in soil. The former is able to be cultivated and thus counted by the plate method, while the latter is not unless it transforms into the former. Based on the results several points required for extensive cataloguing of soil bacteria were noted.     

SNX18 tubulates recycling endosomes for autophagosome biogenesis

The role of membrane remodeling and phosphoinositide-binding proteins in autophagy remains elusive. PX domain proteins bind phosphoinositides and participate in membrane remodeling and trafficking events and we therefore hypothesized that one or several PX domain proteins are involved in autophagy. Indeed, the PX-BAR protein SNX18 was identified as a positive regulator of autophagosome formation using an image-based siRNA screen. We show that SNX18 interacts with ATG16L1 and LC3, and functions downstream of ATG14 and the class III PtdIns3K complex in autophagosome formation. SNX18 facilitates recruitment of ATG16L1 to perinuclear recycling endosomes, and its overexpression leads to tubulation of ATG16L1- and LC3-positive membranes. We propose that SNX18 promotes LC3 lipidation and tubulation of recycling endosomes to provide membrane for phagophore expansion.     

Pollenfertility and seed formation in theOrnithogalum umbellatum/angustifolium complex (Liliaceae/Scilloideae)

The pollen fertility and seed formation of six species of theOrnithogalum umbellatum/angustifolium complex and of seven related species were studied. Four types of pollen grains could be recognized. The pollen fertility varied greatly in this complex and is not related to the ploidy level. The seed formation ofO. umbellatum showed an adaptation to a subcontinental-Mediterranean climate, that ofO. angustifolium to an Atlantic climate. In both cases raindrops seem to be important for pollination, in view of the absence of insect pollinators. After open pollination 113 seedlings were obtained in four species. Their chromosome numbers were determined. Nearly all the cultivated seedlings were aneuploid, which points to a positive selection of euploids in nature, because aneuploid individuals are rare in the wild.Biosystematic Studies on theOrnithogalum umbellatum/angustifolium Complex III.—Previous parts of this series are Part I: Taxonomy. Proceeding Kon. Ned. Acad. Wet. series C,85 (4), 563–574 (1982) andvan Raamsdonk (1984).     

Dynamics of extractable carbohydrates in Pisum sativum. III. The effect of IAA and temperature on content and translocation of carbohydrates in pea cuttings during rooting

The number of roots formed in cuttings of pea ( Pisum sativum L. cv. Alaska) was regulated both by the temperature and by IAA, whereas the time to the appearance of the first roots was regulated only by the temperature. Cuttings treated with 10^-3 M IAA had a smaller content of extractable carbohydrates than the control ones irrespective of the temperature. In the bases of cuttings rooted at 25°C the content of extractable carbohydrates was lower than in those rooted at 15°C. Cuttings treated with IAA showed up to elevenfold increase of extractable carbohydrates in the bases at day 3. This increase of soluble sugars was not correlated with the number of roots formed or the speed of rooting. It is concluded that IAA affects the accumulation of carbohydrates, and this is not connected with the rooting ability of the cuttings.     

Refinement of wingless expression by a wingless- and notch-responsive homeodomain protein,defective proventriculus

Pattern formation during animal development is often induced by extracellular signaling molecules, known as morphogens, which are secreted from localized sources. During wing development in Drosophila, Wingless (Wg) is activated by Notch signaling along the dorsal-ventral boundary of the wing imaginal disc and acts as a morphogen to organize gene expression and cell growth. Expression of wg is restricted to a narrow stripe by Wg itself, repressing its own expression in adjacent cells. This refinement of wg expression is essential for specification of the wing margin. Here, we show that a homeodomain protein, Defective proventriculus (Dve), mediates the refinement of wg expression in both the wing disc and embryonic proventriculus, where dve expression requires Wg signaling. Our results provide evidence for a feedback mechanism that establishes the wg-expressing domain through the action of a Wg-induced gene product.